Capturing the result status of an ALTER command in plpgsql

[jarednevans]

How does one capture the result status of an ALTER command inside
plpgsql code block?
For example:
-----------------
CREATE OR REPLACE FUNCTION public."Setup_P rimary_Keys"()
RETURNS SETOF varchar AS
'DECLARE

BEGIN
ALTER TABLE public."HCM0010 1" ADD CONSTRAINT "hcm00101-pk" PRIMARY
KEY("CUSTNMBR") ;
-- Capture Success or Failure here of the ALTER command
IF [how do I determine success here?] THEN
return next \'HCM00101 primary key set\';
ELSE [eat the failure exception here and continue]
return next \'HCM00101 primary key was not set, continuing with more
code below\';
END IF;
........ more code ........
return;
END;'
LANGUAGE 'plpgsql' VOLATILE;
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